The invention relates to a vibration damper for a hydraulic vehicle brake system with a diaphragm facing the hydraulic fluid that transmits the brake force and being connected to a carrier device by its edge in such manner that it is able to move toward the carrier device or away from it at least slightly in its center area. We would like to refer to DE 195 44 223 A1 for the known state of the art.
It may be required to provide a vibration in a generic hydraulic brake system in order to reduce undesirable vibration in the hydraulic system and/or prevent that small vibration generated by any kind of disruptive force increases to intolerable intensity. Such a vibration damper can also be described as xe2x80x9cpressure smoothening device.xe2x80x9d For this purpose, for example, spring-loaded vibration dampers can be used, which however are very extensive.
A vibration damper as the one described in the above-mentioned publication, which is equipped with a housing or carrier device with a concave recess that is sealed by a disk-shaped diaphragm comprising a spring steel sheet, is considerably simpler. These diaphragms, which are fed on the outside with the hydraulic fluid of the brake system, is welded together with the carrier device on the edge, and the hollow chamber between the diaphragm and the above-mentioned recess is filled with air. Pressure vibration generated in the hydraulic system causes the diaphragm to move into the hollow chamber with its central area and then move away again from the carrier device, which can have a vibration damping effect if appropriately designed.
It has been proven that, in particular, when the diaphragm is relatively thin and therefore weak it can rupture in the most unfavorable case so that the air from the hollow chamber between the diaphragm and the carrier device can reach the hydraulic system. Air pockets in the hydraulic system of a hydraulic vehicle brake system however are known to be extremely undesirable because this can cause a soft braking actuation, caused by the compression of the trapped air.
A task of the present invention is presenting a remedial measure for the described problem. A solution of this task is characterized by the fact that the hollow chamber between the diaphragm and the carrier device that is required for the diaphragm movement is largely evaluated. Beneficial embodiments and further developments are the contents of the sub-claims.
In accordance with certain preferred embodiments of the invention, the mentioned hollow chamber between the diaphragm and the carrier device contains basically a vacuum so that in the case of a destruction of the diaphragm, which cannot be excluded one hundred percent although it is undesirable, no air can reach the hydraulic system. Of course, the vibration damper is no longer functional once the diaphragm has been destroyed, however at least the brake system is not impaired in its function. The vibrations, which can no longer be damped with a destroyed diaphragm, only lead to a loss of comfort because these vibrations can be transmitted onto the chassis of the vehicle, e.g. a passenger car, in the most unfavorable case.
It has been proven that a vibration damper in the hydraulic system of a vehicle brake system can become particularly necessary when the brake pressure in the hydraulic fluid is not too high, i.e. in the range of 5 bar to 20 bar. In order to achieve effective damping, the diaphragm should be relatively thin and flexible. The vacuum existing on the side of the diaphragm facing away from the hydraulic fluid is also beneficial in light of this aspect since this way the vibration damper can take effect already starting at an absolute pressure of 1 bar. In order to prevent the diaphragm from being destroyed at higher brake pressurexe2x80x94it can increase up to about 200 barxe2x80x94the relevant dimensions of the vibration damper can have such a design and the stiffness of the diaphragm be selected in such a way that the diaphragm rests completely against the surface of the carrier device facing toward it at a pressure in the range of 25 bar and more of the hydraulic fluid.
The surface affecting the desired effect, i.e. vibration damping, can therefore be enlarged e.g. with specified dimensions of the carrier device and thus the damping effect can be increased if the diaphragm has a waved or undulated shape in some areas. In order to prevent a destruction of the diaphragm as well, caused by exceptionally high hydraulic pressure, even with such a diaphragm design, the surface of the carrier surface facing toward this area of the diaphragm can have a similar cross-sectional, i.e. basically synchronous, design. For firmness reasons it may be recommended with such a diaphragm design to select the geometric dimensions in such a manner that the distance between the diaphragm without hydraulic pressure and the surface of the carrier device facing toward the diaphragm in the edge area of the diaphragm away from the fastening section (with which it is fastened to the carrier device) is smaller than in the central diaphragm area.
In accordance with a beneficial combination of functions, the carrier device can be a brake piston provided in the caliper of a vehicle brake, against whose side that faces away from the hydraulic fluid a brake lining carrier rests. Such a vibration damper for a hydraulic vehicle brake system is shown as a preferred embodiment of the invention in the only attached FIGURE in a cross-sectional view and is described briefly in the following.